Psychology is commonly understood as the study of the human mind and, therefore, as the science best suited for unpacking human behavior — but this field was not always just about the mind.
The word "psychology" comes from the Greek "psyche," meaning "soul" or "mind."
The first utterance of the word "psychology" in the middle of the 17th century was associated with the study of the soul (the soul being believed in by most pre-Christian philosophers like Plato and Aristotle, for example). But as more so-called enlightened thinking swept through the world and emphasis shifted from spiritual reality to the material world alone, by the middle of the 18th century, psychology became synonymous with merely the study of just the mind.
The rejection of the soul is the foundation of modern psychology, as seen in Wilhelm Wundt, "the father of modern psychology."
Wundt, recognized as the first person to call himself a psychologist, founded the first formal laboratory for psychology in 1879.
Wundt rejected belief in God as the creator and the soul as a part of human nature.
This is why most Christian philosophers and, later, Christian psychologists denied his positions, labeling his works as "psychology without soul."
As Wundt's approach eschewed God and the soul, it stands to reason that he (like the Enlightenment thinkers who strongly influenced him) also rejected the idea of objective truth. In his 1912 book Introduction to Psychology, Wundt wrote, "An idea is no more an even relatively constant thing than is a feeling or emotion or volitional process. There exist only changing and transient ideational processes; there are no permanent ideas that return again and disappear again."
In addition to denying objective truth, Wundt, in his earlier book Outlines of Psychology, equated the animal mind with the human mind: "The mental life of animals shows itself to be in its elements and in the general laws of their combination everywhere the same as that of man."
After Wundt, psychology (as a field of study) disregarded the soul and, for the most part, drew no distinctions between human beings and animals in the endeavor to figure out how the human mind works.
Seeing this error in modern psychology, Bp. Fulton Sheen dedicated much time and effort to correcting these false propositions.
Our nature is not that of a goat or a pig — our nature is rational; we're human beings governed not by the subconscious mind. [We're] governed by a reason and governed by a will. And it's false to say that we can always cure a psychological complex by a physiological outlet. One might just as well say the way to overcome a complex about committing suicide is to jump off the Brooklyn Bridge.
Two of the most famous psychologists of the 20th century are Sigmund Freud and Carl Jung.
Freud believed every man is motivated by pleasure — specifically sex.
Jung, Freud's successor, was not as radical, but his works came from a flat-out denial of the existence of God. He once even claimed, "The human intellect can never answer this question."
Jung's ideas have seeped into Christianity (specifically Catholicism) more than any other modern psychologist's have — and on top of that, today, his ideas are popular among the more conservative psychologists of the day.
Jung, who founded analytical psychology and invented the terms introvert and extrovert, carried on the soulless post-Enlightenment psychological understanding of the human person.
Father Mitch Pacwa, a Catholic theologian and author, says of Jung: "This is the kind of thing where we have to pay close attention, close attention before we use somebody like Carl Jung because his influence on the Faith is not a positive one."
The New York Times summed up Jung's legacy after his death in 1961, saying, "Before Freud and Jung, the Western world was inclined to think of man's conduct in terms of original sin. ... Dr. Jung declare[ed] flatly that this explanation was not good enough."
Today, the American Psychological Association and the American Psychiatric Association, the two biggest institutions in the United States dealing with mental health, promote abortion, gay "marriage," transgenderism and many more intrinsic evils.
The American Psychological Association, on its own website, even gives thanks to the unconstitutional 1973 Supreme Court decision Roe v. Wade, which legalized child murder on demand in the United States.
Likewise, the American Psychiatric Association makes up terms like gender dysphoria, which they define as a "psychological distress that results from an incongruence between one's sex assigned at birth and one's gender identity."